
package com.hc.core.web.token;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import com.hc.core.web.WebConfig;




/**
 *
 * 
 * @see org.apache.struts.util.TokenProcessor
 * 
 */
public class TokenProcessor {

	/**
	 * The singleton instance of this class.
	 */
	private static TokenProcessor instance = new TokenProcessor();

	/**
	 * Retrieves the singleton instance of this class.
	 */
	public static TokenProcessor getInstance() {
		return instance;
	}

	/**
	 * Protected constructor for TokenProcessor.  Use TokenProcessor.getInstance()
	 * to obtain a reference to the processor.
	 */
	protected TokenProcessor() {
		super();
	}

	/**
	 * The timestamp used most recently to generate a token value.
	 */
	private long previous;

	/**
	 * Return <code>true</code> if there is a transaction token stored in
	 * the user's current session, and the value submitted as a request
	 * parameter with this action matches it.  Returns <code>false</code>
	 * under any of the following circumstances:
	 * <ul>
	 * <li>No session associated with this request</li>
	 * <li>No transaction token saved in the session</li>
	 * <li>No transaction token included as a request parameter</li>
	 * <li>The included transaction token value does not match the
	 *     transaction token in the user's session</li>
	 * </ul>
	 *
	 * @param request The servlet request we are processing
	 */
	public synchronized boolean isTokenValid(HttpServletRequest request) {
		return this.isTokenValid(request, false);
	}

	/**
	 * Return <code>true</code> if there is a transaction token stored in
	 * the user's current session, and the value submitted as a request
	 * parameter with this action matches it.  Returns <code>false</code>
	 * <ul>
	 * <li>No session associated with this request</li>
	 * <li>No transaction token saved in the session</li>
	 * <li>No transaction token included as a request parameter</li>
	 * <li>The included transaction token value does not match the
	 *     transaction token in the user's session</li>
	 * </ul>
	 *
	 * @param request The servlet request we are processing
	 * @param reset Should we reset the token after checking it?
	 */
	public synchronized boolean isTokenValid(HttpServletRequest request, boolean reset) {

		// Retrieve the current session for this request
		HttpSession session = request.getSession(false);
		if (session == null) {
			return false;
		}

		// Retrieve the transaction token from this session, and
		// reset it if requested
		String saved = (String) session.getAttribute(WebConfig.TOKEN_IN_SESSION);
		if (saved == null) {
			return false;
		}

		if (reset) {
			this.resetToken(request);
		}

		// Retrieve the transaction token included in this request
		String token = request.getParameter(WebConfig.TOKEN_KEY);
		if (token == null) {
			return false;
		}

		return saved.equals(token);
	}

	/**
	 * Reset the saved transaction token in the user's session.  This
	 * indicates that transactional token checking will not be needed
	 * on the next request that is submitted.
	 *
	 * @param request The servlet request we are processing
	 */
	public synchronized void resetToken(HttpServletRequest request) {

		HttpSession session = request.getSession(false);
		if (session == null) {
			return;
		}
		session.removeAttribute(WebConfig.TOKEN_IN_SESSION);
	}

	/**
	 * Save a new transaction token in the user's current session, creating
	 * a new session if necessary.
	 *
	 * @param request The servlet request we are processing
	 */
	public synchronized void saveToken(HttpServletRequest request) {

		HttpSession session = request.getSession();
		String token = generateToken(request);
		if (token != null) {
			session.setAttribute(WebConfig.TOKEN_IN_SESSION, token);
		}

	}

	/**
	 * Generate a new transaction token, to be used for enforcing a single
	 * request for a particular transaction.
	 * 
	 * @param request The request we are processing
	 */
	public synchronized String generateToken(HttpServletRequest request) {

		HttpSession session = request.getSession();
		try {
			byte id[] = session.getId().getBytes();
			long current = System.currentTimeMillis();
			if (current == previous) {
				current++;
			}
			previous = current;
			byte now[] = new Long(current).toString().getBytes();
			MessageDigest md = MessageDigest.getInstance("MD5");
			md.update(id);
			md.update(now);
			return toHex(md.digest());
		} catch (NoSuchAlgorithmException e) {
			return null;
		}

	}

	/**
	 * Convert a byte array to a String of hexadecimal digits and return it.
	 * @param buffer The byte array to be converted
	 */
	private String toHex(byte buffer[]) {
		StringBuffer sb = new StringBuffer(buffer.length * 2);
		for (int i = 0; i < buffer.length; i++) {
			sb.append(Character.forDigit((buffer[i] & 0xf0) >> 4, 16));
			sb.append(Character.forDigit(buffer[i] & 0x0f, 16));
		}
		return sb.toString();
	}
}
